Tracking system

ABSTRACT

A system simultaneously tracks multiple objects. All or a subset of the objects includes a wireless receiver and a transmitter for providing an output. The system includes one or more wireless transmitters that send commands to the wireless receivers of the multiple objects instructing different subsets of the multiple objects to output (via their respective transmitter) at different times. The system also includes object sensors that receive output from the transmitters of the multiple objects and a computer system in communication with the object sensors. The computer system calculates locations of the multiple objects based on the sensed output from the multiple objects.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/506,969, filed Oct. 6, 2014, which is a continuation of U.S. patentapplication Ser. No. 12/906,012, filed on Oct. 15, 2010, which claimsthe benefit of U.S. Provisional Application No. 61/307,578, filed onFeb. 24, 2010, each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field

The technology described herein relates to tracking objects.

Description of the Related Art

The remarkable, often astonishing, physical skills and feats of greatathletes draw millions of people every day to follow sports that rangefrom the power of football to the speed of ice hockey. Sports fans arecaptivated by the unique abilities of the individual players, as well asthe coordination of the team. Fans have learned that what a player hasdone in the past may affect the player's ability to perform during thepresent. As a result, there has been an interest in tracking players andobjects at sporting events.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a system for trackingobjects.

FIG. 2 is a block diagram of one embodiment of a camera/transmitter podfor use with the system of FIG. 1.

FIG. 3 is a block diagram of one embodiment of a transmitter.

FIG. 4 is a block diagram of one embodiment of an RF Controller.

FIGS. 5A and 5B depict helmets.

FIG. 6 is a block diagram of one embodiment of a circuit that can bepositioned in a helmet.

FIG. 7 is a timing diagram depicting the signals sent from thetransmitters to the helmets.

FIG. 8A depicts one embodiment of an RFID tag system.

FIG. 8B depicts one embodiment of an RFID listening station.

FIG. 9 is a flow chart describing one embodiment of a process foroperating a tracking system.

FIG. 10 is a flow chart describing one embodiment of a process foroperating the Central Computer of the tracking system.

FIG. 11 is a flow chart describing one embodiment of a process performedby the RF Controller.

FIG. 12 is a flow chart describing one embodiment of a process performedby the RF Controller.

FIG. 13 is a flow chart describing one embodiment of a process foroperating the transmitter

FIG. 14 is a flow chart describing one embodiment of a process ofoperation for the electronics in a player's helmet.

FIG. 15 is a flow chart describing one embodiment of a process foroperating the camera.

FIG. 16 is a flow chart describing one embodiment of a process foroperating the Central Computer to calculate three dimensional locations.

FIG. 17 is a flow chart describing one embodiment of a process fordetermining a three dimensional location.

FIG. 18 is a flow chart describing one embodiment of a process fordetermining a three dimensional location.

FIG. 19 is a flow chart describing one embodiment of a process forinitializing a tracking system.

FIG. 20 is a flow chart describing one embodiment of a process forperforming an registration.

FIG. 21 is a flow chart describing one embodiment of a process forperforming registration relative to other sensors.

FIG. 22 is a flow chart describing one embodiment of a process fortracking a ball or other object.

FIG. 23 is a flow chart describing one embodiment of a process fortracking a ball or other object.

FIG. 24 is a flow chart describing one embodiment of a process forautomatically detecting and reporting a concussion or other condition.

DETAILED DESCRIPTION I. Introduction

A system is disclosed that can track one or more objects at an event. Inone embodiment, the system can automatically and simultaneously trackmultiple objects that are moving concurrently. The system can be used atsporting events or other types of events, and is not limited to any typeof event or environment.

One example used below is to track players and a ball at a footballgame. In this example, the players each have a transponder in theirhelmet that responds to a query with an infra-red (IR) pulse. The systemqueries the players in a round-robin fashion, querying the players onthe field more frequently than those on the bench or sidelines.

In one example embodiment, twenty IR cameras (pointed at the field) aremounted at six locations around the football stadium. These cameras aresensitive only to the narrow band of IR emission transmitted by thetransponders in the players helmets. Additionally, the cameras areshuttered to coincide with the transponder pulses. In one example, allcameras open their shutters for 1/10,000th of a second, and they do thistwo hundred times per second. In another embodiment, the system opensthe cameras' shutters one hundred and fifty six times per second. Eachtime the cameras open their shutter, one (or more) of the playertransponders flashes a 1/10,000th second IR pulse. Due to the very fastshutter pulse synchronized with the IR pulse, along with an IR filter oneach camera that permits only the very narrow band of IR transmitted bythe transponders, each of the cameras should see one bright dot (pertarget) on a generally dark background (at least locally dark—it seemsthat in some embodiments the football field can be as bright as theLED—but the non-lit helmet presents a dark background as compared to thehelmet during a flash). In one embodiment, to further distinguish thetransponder from the background, the system uses a differencingalgorithm to subtract an image formed by combining images immediatelybefore and after the target frame from the target frame.

One aspect of this tracking system is the individual addressing of eachobject (e.g. player/helmet) to be tracked. The stadium is to beinstrumented with six RF transmitters in communication with a centralcontrol computer. More or fewer than six RF transmitters can also beused. A Central Computer will send a message out to each of thetransmitters for each IR video frame (e.g., two hundred frames persecond) to indicate which player is to be addressed. These sixtransmitters are distributed around the field to add spatial diversity(and, therefore, robustness) to the RF addressing scheme. Each RFtransmitter in turn will then send out a short message indicating whichhelmet transponder (player) is to pulse, and a countdown indicating thetime that the pulse must occur. This countdown increases addressingrobustness significantly through temporal diversity. The transponderneed only receive a message packet from one of the six transmitters toknow when it is to output a pulse. At the specified output time, each ofthe six transmitter modules will send out a simultaneous pulse to theco-located IR cameras (as many as four, or a different number, at eachtransmitter location). Each IR camera then captures an image while thetarget transponder is outputting its IR pulse, and sends that image toits dedicated co-located computer. The co-located computer finds thetarget (or targets) in the image, and sends the target's pixelcoordinates and description to the Central Computer for tracking.

This active addressing approach allows for automatically trackingmultiple targets simultaneously, and alleviates the need for manualinteraction to identify targets as specific players. The system will use“adaptive” triggering in order to track the most important targets atthe highest temporal resolution. One embodiment includes identifyinglocations for all players on the field five times per second. The systemwill also identify players that are off the field once every twoseconds. In addition, referees and fixed registration landmarks willeach be identified once per second. The moment a player (previously offthe field) is detected as being on the field, that player's frequency oflocation identification will automatically be increased to five timesper second. Other frequencies can also be used.

Alternative embodiments include identifying two or more players in asingle frame if those players cannot be confused from one another (e.g.players on opposite team benches). Another alternative includes moving aplayer up in the list to be identified in the event that player wasn'tidentified in the last round, is carrying the ball, has just undergoneunusually high acceleration, etc. In another alternative, the systemwill modify the sequence by identifying skilled players (e.g.,quarterback) at a higher frequency than others (e.g., linemen).

II. System

FIG. 1 is a block diagram depicting one example system that canautomatically track multiple objects that are simultaneously moving inreal time. The system can be used at a live sporting event or other typeof event. The system is not limited to any particular type ofapplication or event. For example purposes, the system will be describedbelow with respect to an American football game; however, the system isnot limited to an American football game and can be used with many otherenvironments.

FIG. 1 shows football stadium 10 that includes football field 12. Onfield 12 are players 14 and ball 16. In some games, there can bemultiple balls. The system described below will automatically trackplayers 14 and ball 16 as they simultaneously (or not simultaneously)move about field 12 and move off field 12. For example, FIG. 1 showsplayers 14 on field 12 and players 15 off field 12. The players 15 canalso be tracked simultaneously with the players 14. Additionally, thesystem can determine whether the players are on or off the field.

The automatic tracking system includes Central Computer 20 incommunication with a User Interface Computer (UI computer) 22 viaEthernet or RS-232. The system also includes RF Controller 24 incommunication with Central Computer 20 via RS-232, or othercommunication means. Surrounding field 12 are six transmitter/sensorpods (“pods”) 30. Each pod 30 includes one or more RF transmitters andone or more sensors. In one embodiment, each pod 30 includes four IRcameras/sensors. In some embodiments, some of the pods 30 will includefour IR cameras/sensors and other pods will include more or fewer thanfour IR cameras/sensors (e.g. three or five) so that there is a total of20 IR cameras/sensors in the system. Each of the pods 30 willcommunicate with Central Computer 20 via Ethernet (indicated by “E” inFIG. 1). Each of the pods 30 will also communicate with RF Controller 24via an RS-422 line. In one embodiment, an RS-422 line will be connectedto RF Controller 24 and wired throughout the stadium. Each of pods 20can connect to that RS-422 line in a daisy-chain configuration. In someembodiments, the pods are connected in parallel on the RS-422 line.

In general, a human operator will interact with UI Computer 22 to seethe real-time operational results of the tracking system of FIG. 1, andprovide instructions to the system. Central Computer 20 controls theoperation of the automatic tracking system, determines the actuallocations of the objects being tracked and provides commands to theother components in order to perform the tracking. For example, CentralComputer 20 will indicate to RF Controller 24 the frequency with whichvarious objects should be tracked. In one embodiment, Central Computer20 issues each player triggering commands itself. It does this throughthe RF controller, but doesn't tell the controller anything of thefrequency the player will be tracked at. RF Controller 24 will sendcommands to each of the transmitters in pods 30 instructing thetransmitters which players should have their position sensed at whichtime. That information will be transmitted wirelessly using the RFtransmitters in pods 30 to transponder circuits on players 14 and 15. Atthe appropriate times, wireless sensors in pods 30 will detect players14/15 and transmit information about the detection back to CentralComputer 20 via the Ethernet (E) so that Central Computer 20 cancalculate the three-dimensional locations of each of the players 14/15.Details of tracking ball(s) 16 will be provided below.

In one example, pods 30 are located above the field level. For example,they can be mounted in portions of the stadium that are raised above thefield level. In one embodiment, they are positioned around the field toprovide spatial diversity so that all portions of the field are in viewof multiple pods 30.

FIG. 2 is a block diagram depicting one embodiment of the components ofa pod 30. This particular embodiment includes four IR cameras/sensors60, 62, 64 and 66. In one embodiment, the cameras/sensors can be digitalvideo cameras, digital still cameras, analog video cameras or analogstill cameras. In one embodiment, the cameras can be dedicated for IRsensing. In another embodiment, the cameras can be manufactured forsensing a range, or ranges of, wavelengths and filters can be used torestrict the sensing to IR or other specific ranges. In one exampleimplementation, the cameras are Prosilica GE 680 monochrome 640×480digital video cameras that capture up to two hundred frames per secondand transmit that data uncompressed on a 1 GB Ethernet. In oneembodiment, each of the cameras will open a shutter for 1/10,000th of asecond. The CCD of that camera can respond to light in the IRwavelengths as well as other wavelengths. In one embodiment, a band passfilter is placed in front of the lens to only allow IR light at 850nm+/−10 nm. In other embodiments, other cameras can also be used orother types of sensors (e.g., other than cameras) can be used.

Each of the cameras of pod 30 is connected to a dedicated cameracomputer via Ethernet. For example, camera 60 is connected to cameracomputer 70, camera 62 is connected to camera computer 72, camera 64 isconnected to camera computer 74, and camera 66 is connected to cameracomputer 76. In one embodiment, the camera computers 70, 72, 74 and 76are dual core Intel atom-based computers. In one example implementation,each camera computer is a single printed circuit board (andcomponents—and perhaps one or more daughter boards) and pod 30 willinclude a rack with all four boards inserted in the rack. Each of thecamera computers 70, 72, 74 and 76 are connected to a hub (or switch) 80which provides an Ethernet connection E to Central Computer 20.

In one embodiment, each of the football players will be wearing ahelmet. The helmet will instrumented with a transponder. Thattransponder will receive an RF signal from one or more transmitters ofpods 30 instructing that transponder to send out an electromagneticsignal. In response to receiving the RF signal from a transmitter, theappropriate helmet transponder will send out its electromagnetic signalat the designated time. In one embodiment, the electromagnetic signal isa continuous wave infrared burst. Camera 60, 62, 64 and 66 will becommanded to capture an exposure that largely coincides with the timingof the IR signal from the helmet's transponder. One or more of cameras60, 62, 64 and 66 will ideally sense the IR signal from the helmet'stransponder. The IR signal will be appear as a cluster of pixels in thecaptured image of the camera. The output images from cameras 60, 62, 64,and 66 are sent to camera computers 70, 72, 74 and 76 to identify wherein the image the IR signal source is detected. Camera computers 70, 72,74 and 76 will then transmit data packets to Central Computer 20 via theEthernet.

The data packs transmitted from camera computers 70, 72, 74 and 76 toCentral Computer 20 will include the following information: (x,y)weighted centroid of each pixel cluster in CCD coordinates, min and maxextents of each cluster in CCD coordinates, player ID, time, peak pixelvalue in each cluster, “total energy” (this is simply the sum of pixelvalues for the cluster) of each cluster, and camera ID. The player IDidentifies which player the given candidate clusters correspond to, andhas been provided to the camera computer by transmitter 82 (see below).The time is the computer time of the control computer. The brightness isthe highest brightness value of all the pixels in the cluster of pixelsdetected. The total energy is the sum of all brightness values in thecluster of pixels. Each camera has a unique identification, which istransmitted as camera ID. The local computers 70, 72, 74 and 76 alsotransmit diagnostic information to Central Computer 20.

Pods 30 also include transmitter board 82. In one embodiment,transmitter board 82 can receive the RS-422 signal sent out by RFController 24. In one example embodiment, the RS-422 signal is sent on aCat5 table. Note that FIG. 2 does not show the power supply whichprovides power to all the components.

FIG. 3 is a block diagram depicting one example embodiment of thecomponents of transmitter board 82 (see FIG. 2). Transmitter board 82includes an RJ-45 pass-through 102, RS-422 decoder 104, opto-isolationcircuit 106, processor 108, switches 110, radio module 112, and antenna114. RJ-45 pass-through 102 can connect to the Cat5/RS-422 line from RFController 24. RJ-45 pass-through will not change on the Cat5/RS-422line. Rather, it provides a pass-through for the signal and transmits acopy of that signal to RS-422 decoder 104. In one embodiment, RS-422decoder 104 will decode the signal to read the transmitted information.In one embodiment, the transmitted information includes a Pulse signalto be used as a trigger and a Data signal (e.g., commands) to identifywhich players need to be tracked at which times. More information willbe provided below.

The pulse and data information will be transmitted from RS-422 decoder104 to opto-isolation circuit 106, which will provide electricalisolation between the Cat5/RS-422 line and processor 108. The Pulsesignal received by processor 108 from opto-isolation circuit 106 willtell processor 108 when to trigger the cameras in the respective pod 30.The Data signal received by processor 108 from opto-isolation circuit106 indicates which player ID is to be tagged to the resulting clusterdata. Switches 10 are hard switches which provide a unique ID for pod 30or the particular transmitter board 82.

Processor 108 sends a, trigger signal, to each of the cameras 60, 62, 64and 66 in order to trigger the start of the cameras' exposure (e.g.,trigger the camera to capture an image). Processor 108 will also send asignal, player ID, to each of the camera computers 70, 72, 74 and 76indicating to the camera computers which player the cameras are sensingwhen for a given exposure. Processor 108 will also send a signal toradio module 112 indicating which is the next player that should outputan IR pulse to be sensed by the cameras. Radio module 112 will send outthat information as an RF signal via antenna 114. In one embodiment,processor 108 is an Atmel Atmega 48P processor, the trigger signal andplayer ID signal are serial signals, and radio module 112 is a CC2520from Texas Instruments. Other hardware can also be used. In alternativeembodiments, radio module 112 can be replaced with an IR transmitter sothat the data can be transmitted to the helmets (or other objects) usingIR signals. The RF signal will be sent out at an amount of timepreceding the commanded IR pulse that is determined by the switchpositions (which indicate the node ID).

FIG. 4 is a block diagram depicting one example embodiment of thecomponents of RF Controller 24 (see FIG. 1). In one embodiment, RFController 24 includes a processor 140 and RS-422 encoder 142. Oneexample of a suitable processor is an Atmel ATTINY 2313 processor. Inone embodiment, processor 140 communicates with Central Computer 20 viaan RS-232 line in order to receive commands and other information,described below, that indicates the timing of when various playersshould be tracked. Processor 140 will then create two signals: Pulse andData. The Pulse signal commands the beginning of the exposure of thecameras and when the helmet transponders should output an IR pulse to bedetected by the cameras/sensors. The Data signal from processor 140indicates which is the next player to be sensed. Both the Pulse and Datasignals are sent from processor 140 to RS-422 encoder which encodes thesignals onto an RS-422 signal to be sent on the Cat5 line to the pods30.

The Cat5 cable has four pairs of wires. One pair is used for the Pulseand one pair is used for the Data. The other two pairs are grounded. ThePulse signal is a square wave. The data signal will include a player ID.The player ID can be a number or other alphanumeric character. Togenerate the Pulse signal, processor 140 will be used to create a highprecision clock signal in order to appropriately time the Pulse signal.

As discussed above, in one embodiment, each of the players will wear ahelmet with a transponder positioned in the helmet. In some embodiments,there will also be transponders in the referees' hats as well as fixedtransponders on or around the field for automatic registration). FIGS.5A and 5B provide two embodiments of helmets. Inside the helmet will bea helmet transponder circuit. This circuit will include a set of IRemitting LEDs. In one embodiment, the LEDs can be manufactured tospecifically output IR energy only. In other embodiments, the LEDs canbe manufactured to transmit at various wavelengths and a filter can beplaced over the LEDs so that only IR spectrum (or some portion thereof)is transmitted In some embodiments, it is desirable that the output ofthe LEDs is electromagnetic signals that are not in the visible spectrumso that these LEDs do not interfere with the game or event.

The circuit inside the helmet will be mounted on a circuit board andthat circuit board will be mounted in a location in the helmet that willnot interfere with the player or the player's safety. For example, manyhelmets have padding, and the circuit board can be placed underneath orbetween padding. The LEDs will be mounted to the helmet shell. In oneembodiment, holes will be drilled in the helmet from the exteriorsurface of the helmet to the interior surface of the helmet. The LEDswill be positioned in these holes, recessed from the surface of thehelmet. A clear coating will be in front of the LEDs, at the surface ofthe helmet, to protect the LEDs. This protective layer may have anappearance that will minimize the visual impact of the LED, but will belargely transparent to the IR wavelengths in question. In oneembodiment, the clear coating can be a clear urethane adhesive. The backof the LEDs will include wires to the circuit board. In one embodiment,each helmet will have twenty four LEDs that are narrow bandwidth LEDsthat transmit IR at approximately 850 nm+/−20 nm. One example LED is aVishay TSHG-6400.

In the embodiment of FIG. 5A, the LEDs are arranged as a crown aroundthe helmet at 17 degrees above the horizon. In the embodiment of FIG.5B, the LEDs are arranged as four clusters of six LEDs per cluster. Twoclusters are on one side of the helmet and two clusters are on the otherside of the helmet. On each side of the helmet, there is one cluster infront of the typical logo position of the helmet and one cluster behindthe logo position of the helmet. The helmet of FIG. 5B does not show alogo, but in many instances the logo is in the center of the side of thehelmet. Other arrangements for the LEDs, in addition to those depictedin FIGS. 5A and 5B, can also be used. Note that in one embodiment, eachof the clusters of LEDs is electrically in parallel to each other.Within each cluster, there are two sets of LEDs electrically in parallelwith each other. Each set has three LEDs in series.

FIG. 6 is a block diagram depicting one example embodiment of thecomponents of the helmet transponder circuit that is mounted inside thehelmet of the player. In this example, the helmet transponder circuitincludes an antenna 180, radio module 182, processor 184, switch 186,LEDs 188, batteries 190, voltage regulator 192 and accelerometers 194 Inone embodiment, processor 184 is an MSP430 from Texas Instruments andradio module 182 is a CC-2520 from Texas Instruments, and switch 186 isa field effect transistor. Processor 184 is connected to radio module182, switch 186 and voltage regulator 192. Switch 186 is also connectedto ground and LEDs 188.

Radio module 112 of transmitter 82 in pods 30 sends out an RF signalwith data via antenna 114. That signal, which indicates which helmettransponder should output an IR pulse, is broadcast to all the helmettransponders on the field. Therefore, every player is capable ofreceiving that transmission. Because there can be reasons why aparticular helmet transponder will not receive a transmission from aparticular transmitter, as discussed above, there are sixtransmitter/sensor pods so that there are six transmitters transmittingthe same information (at different times). Each of the helmets willreceive the six signals (or less than the six signals) via antenna 180and radio module 182. The data received will be sent to processor 184.Based on the signal received at processor 184, the processor willdetermine whether it is the particular helmet transponder circuit's turnto transmit its IR pulse. When it's time for the helmet transponder totransmit an IR pulse, processor 184 will actuate switch 186 to turn onLEDs 188 for 1/10,000th of a second. LEDs 180 are also connected tobatteries 190. Voltage regulator 192 provides power to radio module 182and processor 184 from batteries 190.

FIG. 6 also shows a set of set single axis accelerometers 194. In otherembodiments, multi axis accelerometers can also be used. Theseaccelerometers 194 are distributed around the head of the player byappropriately mounting them in the helmet. The accelerometers allowprocessor 184 to automatically determine whether a potentially dangerousimpact has occurred (e.g., causing a concussion). The use of theaccelerometers allows the transmission of such impact data in real time(or near real-time).

FIG. 7 is a timing diagram describing the operation of transmitter board82 with respect to transmitting information to helmet transpondercircuits (see FIG. 6). The first signal depicted in FIG. 7 is thetrigger signal. This is the signal provided by transmitter 82 as triggerto each of the cameras 60, 62, 64 and 66 (see FIG. 2). The triggersignal can be the same as or based on the Pulse signal sent from RFController 24 to each of the transmitter boards B2.

At the same time the Pulse signal is sent to the transmitter boards 82from RF Controller 24, the data is also sent. The Pulse signal indicateswhen to pulse for the last set of data. The data sent with the pulseindicates what is the next helmet that will transmit when the next timethe pulse is provided. Each of the transmitters will receive that dataand broadcast that data using a digital signal over a 2.4 GHz (WiFi)direct sequence spread spectrum signal. To provide temporal diversity,each of the six transmitters (e.g., one transmitter per pod 30, and sixpods 30) will transmit at different times, as depicted in FIG. 7. Forexample, TX0 shows the signal from transmitter 0, TX1 shows the signalfrom transmitter 1, TX2 shows the signal from transmitter 2, TX3 showsthe signal from transmitter 3, TX4 shows the signal from transmitter 4and TX5 shows the signal from transmitter 5.

When each of the signals depicted in FIG. 7 are low, no signal is beingsent. When FIG. 7 shows the signal high, data is sent. In oneembodiment, each transmitter will send three pieces of data: a playerID, the time to pulse and timing information in order to start countingthe time to pulse. In one embodiment, the timing information is apredetermined rising edge of a part of the signal (e.g. first risingedge, or different rising edge). The time to pulse information willprovide an indication of the time between the rising edge of the timinginfo and the rising edge of the next trigger signal. Because eachtransmitter transmits at different times, that time to pulse informationwill be different for each transmitter, however, the player ID(s)transmitted from each transmitter will be the same. FIG. 7 shows eachtransmitter transmitting at a different time. In one embodiment, eachtransmitter will start its transmission 800 μs after the previoustransmitter started its transmission. For example, transmitter TX0 willstart its transmission 800 μs after the start of the trigger,transmitter TX1 will start its transmission 800 μs after the start ofthe transmission from TX0, transmitter TX2 will start its transmission800 μs after the start of the transmission form TX1, etc. The bottomsignal of FIG. 7 is the signal received by an example helmet transpondercircuit. This shows the helmet receiving transmissions from all sixtransmitters. In some instances, the helmet will receive informationfrom a subset of transmitters. By using multiple transmitters atdifferent locations at different times, the system provides a level offault tolerance.

The system also includes multiple options for tracking ball 16 (or otherobjects). Many of these embodiments will be discussed below. In oneembodiment, the system uses an RFID tag in ball 16. FIGS. 8A and 8Bprovide example embodiments of hardware used to implement the RFID tag.For example, FIG. 8A shows ball 16 with an RFID tag 208 embedded in ball16. For example, the RFID tag can be between the bladder and leather ofthe ball. RFID tag 208 can also be mounted in other portions of theball. In one embodiment, each player will have one or more RFID tagreading circuits positioned on the player. For example, the RFIDcircuits can be positioned on shoulder/chestpads, pants, the helmet,elbow pads, gloves, wristbands, etc. A player could have one RFID tagcircuit or multiple RFID tag circuits.

In one embodiment, an RFID tag circuit includes controller 200 incommunication with sensor 202 and radio module 204. The radio module 204is connected to antenna 206. Sensor 202 can be any standard RFID tagreader known in the art that is small. Controller 200 can be anysuitable processor known in the art. Radio module 204 can be CC2520 fromTexas Instruments, or another suitable radio module. The system willalso include a battery/power source.

In embodiments that have multiple RFID tag circuits mounted on a player,each of the RFID tag circuits can include its own sensor, controller andradio module. In other embodiments, each RFID tag circuit will includeits own sensor and controller, but will share a common radio module. Inother embodiments, each RFID tag circuit will include its own sensor,but will share a common controller and radio module. The multiplesensors should (but are not required to be) distributed throughout theplayer's body. Sensor 202 is used to automatically sense that tag 208 isin proximity of sensor 202. In other words, sensor 202 is used todetermine that the ball 16 is in proximity to player 14. Upon detectingthe presence of tag 208, the sensor will provide a signal to controller200 which will instruct radio module 204 to send a signal (via antenna206) indicating: current time, an ID for sensor 202 and an ID for tag208. In one embodiment, tag 208 will transmit its ID to sensor 202. Fortracking the ball, the time can be sensed at the listening station(helmet, sideline, etc.), and the ball ID will most likely not beneeded.

In one embodiment, will be a set of listening stations positioned aroundfield 12. FIG. 8B depicts an example listening station. In oneimplementation, the listening stations can be at field level; however,other positions can also be utilized. Each listening station willinclude a computer 220 connected to a radio module 222. Via antenna 224,radio module 222 can receive signals from radio module 204 of the RFIDtag circuits on players indicating that a player has sensed the presenceof the ball in proximity to the player. That information will beprovided to computer 220, which will transmit the information to CentralComputer 20 via Ethernet. More details of the ball tracking will beprovided below. Alternatively, the RFID receiver may use Bluetooth (orsimilar) to transmit the signal to the helmet—which will effectivelyrelay the signal further (to the field receivers, or to the 6 nodesdiscussed above).

In the above discussion, football was used as an example. Anotherexample can include tracking hockey players and an ice hockey puck. Anexample of tracking an ice hockey puck is found in U.S. Pat. No.5,862,517, incorporated by reference herein in its entirety. Whentracking hockey players, the electronics described for the footballhelmet can also be placed in the hockey helmet. Alternatively, theelectronics can be placed on top of the hockey helmet in a channel,commonly found on hockey helmets. Additionally, in an alternativeembodiment, the hockey helmet may only include six LEDs on top of thehelmet because it is possible to put a set of cameras on thecatwalk/rafters at the top of the arena. Other types of objects can alsobe tracked.

III. Operation

FIG. 9 is a block diagram describing one embodiment of the operation ofthe system described above. In step 302, the system is registered. Inorder to track moving objects, the system needs a reference from whichto identify locations. Registration provides that reference, asdescribed below, and appropriately calibrates the system in light ofthat reference. In step 304, the system will automatically trackplayers/objects that are simultaneously moving and store that trackingdata. In step 306, the system will report the tracking data. Althoughthe steps in FIG. 9 are shown in a particular order, the steps do notnecessarily need to be performed in that order. That is, the process ofregistering the system can start prior to step 304 and then alsoperformed during step 304 and 306. Similarly, step 306 can be performedduring or after step 304. Reporting the tracking data, step 306 includesstoring the data in a relational database, creating an animationdepicting the motion of the various objects being tracked,highlighting/enhancing various moving objects in video or still images,reporting about the motion via alerts, text messages, e-mails, etc. U.S.Pat. No. 5,912,700, incorporated herein by reference in its entirety,provides a suitable example of using tracking data to highlight/enhancevarious moving objects in video.

FIG. 10 is a flowchart describing one embodiment of the operation ofCentral Computer 20 when tracking players/objects and storing trackingdata (step 304 of FIG. 9). In step 330 of FIG. 10, Central Computer 20will send out initial commands/instructions to RF Controller 24indicating times for the helmet transponders to transmit the theirrespective IR pulses. In step 332, Central Computer 20 will determinethree-dimensional locations of each of the objects being tracked. Instep 334, Central Computer 20 will determine which players/objects 14are on the field 12 and which players/objects 15 are off the field. Thisis used to determine the frequency for sampling data for each of theplayers. Central computer 20 can determine which players are on thefield and which players are off the field by comparing thethree-dimensional locations of the players to the known location of thefield. In step 336, Central Computer 20 may (optionally) dynamicallychange the commands/instructions to RF Controller for indicatingfrequency or timing of obtaining data from each of the helmettransponders.

After step 336, FIG. 10 shows the process looping back to step 332 sothat the method can repeat. In some embodiments, the order of the steps332-336 can vary so that one or more (or a portion) of the steps can beperformed concurrently or in a different order. In one embodiment,Central Computer 20 will dynamically change the commands based on one ormore occurrences in the event being monitored by, for example, adding orremoving one or more objects from the commands sent to the RF Controlleror changing the frequency that various objects are tracked. For example,as discussed above, players determined to be on the field are tracked ata first frequency and players determined to be off the field are trackedat a second frequency. Based on determining which players are on thefield and which players are off the field, the groups of players beingtracked at the first frequency may be changed and the group of playersbeing tracked at the second frequency may be changed. The processes ofsteps 332-336 are performed automatically so that Central Computer 20will automatically choose the first set of players to track at the firstfrequency and the second players to track at the second frequency. Forexample, if a player walks off the field, then that player is moved fromthe group being tracked at the first frequency to the group beingtracked at the second frequency. Other events can also be used totrigger the changing of frequencies or the changing of players to betracked. For example, if the player has the ball, that player may betracked/identified more frequently. Similarly, certain players who areskilled players may be tracked more frequently. In another embodiment,the system can track players more frequently based on their proximity tothe ball. In another embodiment, based on location on the field,different players can be tracked at different frequencies. For example,if a player known to be a quarterback lines up in a different position,that player will then be tracked with greater frequency.

FIG. 11 and FIG. 12 are flowcharts describing two operations performedat RF Controller 24. In one embodiment, these two processes areperformed in parallel. In step 360 of FIG. 11, RF Controller 24 willreceive instructions from Central Computer 20. In step 362, RFController 24 will update its queue based on the instructions receivedin step 360. As discussed above, in one embodiment the system will trackplayers five times per second if they are on the field and one every twoseconds if they are off the field. There are multiple embodiments thatcan be used.

In one embodiment, Central Computer 20 will create the queue of commandsand will send the commands from the queue in sequence to RF Controller24 in step 360. Each command will identify a player ID. In one example,the commands are sent when Central Computer 20 wants RF Controller toforward them. In another embodiment, the commands are sent with anindication of a time to send them. In another embodiment, the commands(with player IDs) are sent in the sequence desired by Central Computer20 and RF Controller 24 knows to forward the commands at predefined timeintervals. RF Controller 24 receives the commands and populates the datainto its own queue in step 362. The queue populated in step 362 is alist of IDs in sequence. Thus, in this embodiment, FIG. 11 is the flowchart describing the population of the queue.

Central Computer 20 will send two hundred commands for each second. Thecommands indicate the sequence (and implicitly the frequency) ofsensing. If a player is to be sensed five times a second, then thatplayer's ID will be sent in five of the two hundred commands for aspecific second, and likely to be spaced apart by approximately ⅕ of asecond.

In another embodiment, Central Computer will not explicitly command eachIR pulse, but will instead command the sequence of transponder ID's tobe pulsed. It will then send updates to the sequence as necessary, andmay send specific trigger commands, or a completely new sequence.

In another embodiment, Central Computer 20 will send commands to RFController 24 indicating the frequency for each player ID. Thatinformation will be kept in a data structure on RF Controller 24. Thatdata structure will be used to populate a queue of commands to be sentto the various transmitter boards 82 of pods 30. That queue is kept onRF Controller 24 and populated as part of step 362. When certain eventsoccur during the game, Central Computer may automatically anddynamically update its commands to change the frequency of sensing forsome players/objects, add new players/objects to the sensing or removeplayer/objects from the sensing.

FIG. 12 is a process describing how the queue is used to send out theData and Pulse to the various transmitter boards 82 of pods 30 from RFController 24. In step 380, processor 140 will access the next player IDin the queue. Note that in one embodiment, processor 140 includes itsown internal storage, or can use external storage. In step 382, the Datais created, indicating the player ID(s). In step 384, the Data and asynchronized pulse are provided to RS-422 encoder 142, and thentransmitted via the Cat5/RS-422 signal to the various pods 30, asdescribed above. After step 384, the process loops back to step 380 andit accesses the next player ID in the queue after waiting an appropriateamount of time based on the desired frequency.

Thus, the queue will indicate a list of player IDs in the order to betransmitted such that IDs for players on the field will be transmittedfive times a second and IDs of players off the field will be transmittedonce every two seconds. There can be some time slots with no sensing.The order of the players IDs will be arranged such that the polling ofeach of the players is temporally spaced apart in equal or close toequal periods.

FIG. 13 is a flowchart describing one embodiment of the operation oftransmitter board 82. In step 402, transmitter 82 will receive the Pulseand Data from RF Controller 24. In step 404, transmitter 82 will sendthe trigger signal to each of the cameras 60, 62, 64 and 66 (see FIG.2). In step 406, transmitter 82 will send the previous player ID tocamera computers 70, 72, 74 and 76. That is, the previous player ID sentto the helmets will be sent to the camera computers 70, 72, 74 and 76 instep 406 so that the camera computers know the helmet that transmittedthe signal received by cameras 60, 62, 64 and 66 when the trigger signalwas asserted. In one embodiment, steps 404 and 406 can be performedsimultaneously or in opposite order. In step 408, transmitter 82 willwait for the predetermined time after the pulse. As described above, thetransmitters will wirelessly broadcast RF signals indicating whichhelmet to pulse next and a time to pulse. As indicated by FIG. 7, eachof the transmitters send the information at different times. Step 408includes each transmitter waiting for its appropriately allotted time totransmit (e.g. as per the timing of FIG. 7). In step 410, when it is theappropriate time to transmit, that transmitter 82 will wirelesslybroadcast the command to multiple players (or other objects) instructingthe particular player/helmet to output at the specified time.

The process of FIG. 13 is performed in response to each set of Data andPulse received from RF Controller 24; therefore, the process of FIG. 13is performed (in one embodiment) two hundred times a second. Thus, overa period of one second, the transmitter is sending commands thatinstruct different subsets of players to output at different times. Inthe embodiment where one player pulses at a time, the subset includesone player. In alternate embodiments, multiple players can pulse at thesame time, and in those cases the subset of players instructed to outputwould include multiple players. In some embodiments, the system willsometimes pulse only one player, and will other times pulse multipleplayers.

FIG. 14 is a flowchart describing the operation of the helmettransponder circuit of FIG. 6. In step 440, the system will continuouslylisten for data. As discussed above, the various transmitters 82 willbroadcast data at predetermined times and the helmet transponder circuitwill constantly listen for that data in step 440. When data is receivedin step 442, the helmet transponder circuit determines whether there isan address match. The data broadcast by the transponder 82 includes aplayer ID. Each helmet has a player ID. If the player ID broadcastmatches the player ID stored in the helmet transponder circuit (step444), then the helmet transponder circuit will count down to theappropriate time in step 446. As discussed above, informationtransmitted from the transponder indicates a synchronization point and atime from the synchronization point for the helmet to transmit. Step 446includes counting down until the time for the helmet transponder circuitto transmit. As shown in the bottom line of FIG. 7, it is possible for ahelmet to receive information from multiple transmitters. If thishappens, the helmet transponder will discard the information receivedfrom other transmitters and only act on the data from the last validtransmission received. Therefore, it is possible, in step 446, that aprevious countdown will be aborted. In step 448, when it is time for thehelmet transponder to transmit its signal, it will pulse its LEDs, asdescribed above. If it was determined, in step 444, that the broadcastplayer ID does not match the stored player ID, then the helmet will nottransmit in this cycle (see step 452).

FIG. 15 is a flowchart describing one embodiment of the operation ofcameras 60, 62, 64 and 66 and camera computers 70, 72, 74 and 76. Instep 502, the cameras will receive a trigger signal from transmitter 82.In step 504, the cameras will sense an electromagnetic signal from thehelmet transponder by capturing an image. The image will likely includeone or more clusters of bright pixels. For example, the image will beall black (i.e. pixel values will be below a specified threshold) withone bright cluster of pixels representing the transmitting helmettransponder. That cluster of pixels will likely have multiple pixels(because of the arrangement of LED's on the ball and helmet, it maycreate two clusters in the image). Some cameras will not detect thetransmitting helmet. The image will be transmitted from the camera tothe appropriate camera computer in step 506. In step 508, the cameracomputer will receive the player ID from the transmitter, as discussedabove. Note that the order of steps 502-508 can be changed from thatdepicted in FIG. 15.

In step 510, camera computer will apply one or more filters to the imagereceived from the camera. For example, a noise filter can be used toreduce noise in the image. In one embodiment, the noise filters will bein the form of a threshold. The threshold may be applied before or afterframe differencing. Additionally, 2D filters can be used (these describeareas on the CCD that correspond to known or likely false targets).Prior to operation, an operator can obtain images from each of the IRcameras or use mathematics to determine the field of view of the IRcameras and determine portions of the field of view of the IR camerathat is impossible for a player to be in or areas of the field of viewwhere the system does not want to track players. Using that information,rectangular portions of the image can be identified in the camera'sfield of view for which data should always be discarded (in otherembodiments, these regions need not be rectangular). In step 512 of FIG.15, the camera computer will find the cluster(s) that most likelycorrespond to the player or object which transmitted the electromagneticsignal (e.g., IR). For example, the system will find the bright clusterof pixels in the black (typically differenced) image and identify the(perhaps weighted) center pixel of the cluster of pixels. In step 514,the system will determine the peak brightness of the cluster of pixelsby identifying the pixel with the greatest brightness value. In step516, the camera computer will determine the total energy of the clusterof pixels by adding up the brightness values for all the pixels in thecluster of pixels. The system may also compute the average intensity bydividing the total energy by the number of pixels in the cluster. Instep 518, camera computer will read the current time. In step 520, thedata message will be created that includes the x and y position of thecenter pixel of the cluster of pixels, the player ID, the time, thebrightness of the cluster of pixels, the total energy of the cluster ofpixels, and the ID for the camera. In step 522, that data message istransmitted to Central Computer 20 using the Ethernet connection (viahub 80). In one embodiment, the data message does not include a timestamp. Rather, the central computer checks that each camera computermessage describes the cluster ID's expected, and nominally expects eachmessage to correspond to the most recent request.

FIG. 16 is a flow chart describing one embodiment of a process fordetermining the three dimensional location of an object (e.g. player14). The process of FIG. 16 is performed by Central Computer 20 as partof step 332 of FIG. 10. In step 550 of FIG. 16, data messages for ahelmet transponder/player are received at Central Computer 20 from thecamera computers 70, 72, 74 and 76 of the various pods 30. These datamessages are sent to Central Computer 20 from the camera computers instep 552 of FIG. 15. In step 552, the received data messages are storedin one or more data structures. In step 554, Central Computer 20calculates a three dimensional location (e.g., x, y, z coordinates) forthe moving object (e.g., player 14) based on data messages from multiplecameras. More details of step 554 are provided below.

In step 556, one or more filters are applied to the three dimensionallocation calculated in step 554. Two examples of filters include regionof interest filters and exclusion zones. Region of interest filters aresoftware methods that discard or ignore data that indicate a locationoutside the region of interest (e.g. players on the sidelines may beoutside of the region of play, but inside *a* region of interest). Forexample, prior to the sporting event, the system can be programmed withthe three-dimensional coordinates that describe the football field,hockey rink, basketball court, etc. These are 3D or volumetric filters,and therefore account for Z-coordinate as well. Thus the region ofinterest may include the volume from field level to 8′ above the fieldmatching the lateral extents of the field. For the ball, the region ofinterest may extend to 50′ height or greater to allow for tracking aball in flight. Additionally, there may be different regions of interestdefined either for convenience/simplicity of shape, or to reflect theexpected region for a given player at a given time. The sideline regionfor example may be used to track players on the bench, while the regionabove the field may be used for active players. Regions of interest maybe dynamic as well—perhaps defined by the last known location of aplayer and the maximum speed he might be expected to move. In oneembodiment, the field of play will include the sidelines, teams benches,and anywhere else that the players or ball are allowed to be and it isdesired to track. Any data indicating a location of a player outside ofthese limits will be ignored (or perhaps regarded as less likely toindicate a valid target).

Exclusion zones are known areas of false data. For example, there may bea camera with a light near the field, or any other light near theplaying surface. It is common for these lights to emit IR energy. Sincethe existence and locations of these sources are known, they can beremoved from the data considered by the Central Computer whendetermining the three-dimensional location. One method for ignoring thecandidates falling within an exclusion zone is after determining thethree-dimensional location of the object, if that location is in anexclusion zone, then ignore that determination of the three-dimensionallocation. For example, in some instances, the system determines one ormore possible locations of the object. If any of these locations are inthe exclusion zone, that location is removed from consideration.Alternatively, Central Computer 20 can ignore all lines of position thatpass (or substantially pass) through an exclusion zone (see discussionof lines of position, below). This would amount to a 2D exclusion zone.This could be done at the camera computers or at the central computer.The exclusion zone can be manually entered at one of the processors oran operator in the production center can identify the exclusion zoneusing an input device (e.g. mouse) in connection with a monitor (videoor sensor data).

In step 558, Central Computer 20 will remove any calculated threedimensional locations that are not likely to be accurate in light ofhistorical data. For example, the historical data can be used to track apath of movement. If the object suddenly moves too far in too short atime, the later data can be ignored (or weighted less heavily until aconsistent pattern emerges). Consider if a player is running on thefield from the twenty yard line to the thirty yard line, and then thenext calculated three dimensional location a fraction of a second lateris in the end zone (e.g., 70 yards away). The newly calculated threedimensional location a fraction of a second later that is in the endzone can be removed from consideration. In step 560, the calculatedthree-dimensional location (if not removed in steps 556-558) is storedby Control Computer 20.

The process of FIG. 16 is performed for each set of samples of eachobject being tracked. A set of samples are all of the cluster of pixelssimultaneously detected for an object by all of the cameras/sensorsdetecting that object at that time. Therefore, in one embodiment, theprocess of FIG. 16 is started two hundred times each second.

FIG. 17 is a flow chart explaining one embodiment for calculating athree dimensional location of an object (e.g., player) based on datafrom multiple cameras/sensors (step 554 in FIG. 16). In step 680 of FIG.17, Central Computer 20 determines a line of position (LOP) for clusterof pixels detected by each sensor. Thus, if there are twenty cluster ofpixels transmitted to Central Computer 20 for a given helmettransponder, twenty LOPs are determined. The LOP is first calculated in“camera space,” the coordinate system in which the IR camera/sensor isat the origin looking along the negative Z axis, with the X axisextending to the right and the Y axis extending upward. The 3dimensional LOP vector is then transformed into the coordinate system ofthe stadium.

In order to calculate the LOP in camera space, the sensor focal length,aspect ratio, and optical distortion are measured. This measurementindicates that a target a meter away if moved one pixel to the sidemoves h meters in space, and if moved one scan line up or down, moves vmeters in space. From these ratios, given that the cluster is x pixelsand y scan lines from the center of the sensor field of view, a vectoris constructed:

V=(x*h,y*v,1.0)

A line of position is represented as a point (P) and the vector (V):

LOP=P,V

The LOP is a parametric representation of a line, since any point on theline can be represented as:

p=P+k*V,

where k is a scalar.

An LOP is transformed into the three dimensional coordinate system ofthe arena by a 4×4 matrix (or by using a 3×3 rotation matrix and a knowntranslation). The three element vector is multiplied by the inverse ofthe upper left 3×3 matrix of the 4×4 transformation matrix. The fourelement point is multiplied by the inverse of the 4×4 transformationmatrix.

For a rigidly mounted IR camera/sensor, an example transformation matrix(J)

J=TYPR

where,

$T = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\{- x} & {- y} & {- z} & 1\end{bmatrix}$ $Y = \begin{bmatrix}{\cos \mspace{14mu} {yaw}} & {{- \sin}\mspace{14mu} {yaw}} & 0 & 0 \\{\sin \mspace{14mu} {yaw}} & {\cos {\mspace{11mu} \;}{yaw}} & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}$ $P = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & {\cos \mspace{14mu} {pitch}} & {{- \sin}\mspace{14mu} {pitch}} & 0 \\0 & {\sin {\mspace{11mu} \;}{pitch}} & {\cos \mspace{14mu} {pitch}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}$ $R = \begin{bmatrix}{\cos \mspace{14mu} {roll}} & 0 & {\sin {\mspace{11mu} \;}{roll}} & 0 \\0 & 1 & 0 & 0 \\{{- \sin}\mspace{14mu} {roll}} & 0 & {\cos \mspace{14mu} {roll}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}$

Since the IR sensor is in a fixed position, the yaw, pitch and roll canbe measured, estimated or derived during the registration process,described below.

After lines of position are determined for every cluster of pixels,Central Computer 20 groups all possible pairs of LOPs (step 682). Foreach pair of LOPs, Central Computer 20 finds the closest point ofapproach of the two LOPs (step 684). If the LOPs do not intersect theclosest point of approach will be two points, one on each LOP. The lineconnecting the two points is perpendicular to both LOPs. To simplify thecalculations, one embodiment contemplates using the midpoint of the lineperpendicular to both LOPs as the closest point of intersection.However, both points can be used in the steps described below.

At the end of step 684, Central Computer 20 now has a set of points ofclosest approach. This set of points may fall into one or more groups—or3D clusters. There will be a threshold for closest approach of twoLOP's, and a threshold for distance between points that can beconsidered in the same 3D cluster. In step 686, Central Computer 20groups the candidates into one or more 3D clusters, and then finds theweighted centroid for each such cluster. The center may be the averageof the coordinates of the points of closest approach, or may be weightedbased on proximity to most recently tracked position for this target,distance of closest approach of the LOP's from which it came, etc. Instep 688, Central Computer calculates a sphere around the center point.The radius of the sphere is predefined. The radius should be big enoughto allow the system to function, but small enough so that improper datais thrown out. In one embodiment, the radius is set as one meter;however, other values can be used. Each time the system is set up, auser may need to use trial and error to determine the proper radius. Instep 690, Central Computer 20 determines whether all the points fitwithin the sphere. If not, Central Computer 20, in step 692, removes thefurthest point and loops back to step 686. If all the points do fitwithin the sphere, then the average or center of the sphere is acandidate for the three-dimensional location of the object.

One alternative is to reduce the radius for each iteration, continueiterating until the minimum radius is reached (e.g. 0.1 meter) and ifthere are a predefined number of points remaining (e.g. 0.2) then avalid three dimensional location candidate has been found. Anotheralternative includes reducing the radius for each iteration, removingall points outside the sphere for each iteration, continue iteratinguntil the minimum radius is reached (e.g. 0.1 meter) and if there are apredefined number of points remaining (e.g. >2) then valid threedimensional location candidate has been found. The points of closestapproach may form more than one separate group of points, in which casethe method of FIG. 17 can be repeated for each group of points and morethan one location candidate will be determined. The incorrect candidatesshould be removed when applying filters in step 556 of FIG. 16.

FIG. 18 is a flow chart describing another method for determining athree dimensional location of an object (step 554 of FIG. 16) that isbased on the probabilities of finding the object at certain locationsalong or near the lines of position. In step 696, lines of position aredetermined for each cluster of pixels of each camera/sensor for theparticular object under consideration. In step 698, the systemdetermines cones for each line of position. That is, each line ofposition can be thought of as a set of cones, one inside the other. Eachcone represents a space with an assigned probability for the objectwithin that space. In step 700, a set of cubes are figuratively created.A first layer of cubes lie on the playing surface. A second layer ofcubes are located above the first layer, and so on. Each cone isprojected such that it passes through one or more cubes. For each lineof position, the probability for a given cube is proportional to thecube's distance from the cone's axis. If more than one cone for aparticular line of position passes through a cube, the cube is assignedthe probability of the highest probability cone passing through it. If acube lies within cones from more than one line of position, a cube willbe assigned more than one probability. Each of the probabilitiesassigned to each cube are added (or multiplied, etc.) and the result isstored for each cube (step 702). If a cube was assigned only oneprobability, then that one probability is the stored result. The cubewith the highest probability is assumed to be the cube where the objectis (step 704). In one embodiment, the cubes are small enough so that theresolution of the cube is sufficient to find the object in oneiteration. In one alternative, the playing surface is divided into asmall set of larger cubes and step 704 determines which of the largecubes the object lies in. Since the resolution of the cubes is not fineenough for the object location determination to be accurate, the processis repeated (in step 706) by looping back to step 700, dividing the onecube which contains the object into smaller cubes, the probability isadded up for each of the smaller cubes and the system determines whichof the smaller cubes contains the object. If the resolution of the smallcube is sufficient, the method ends; otherwise, the method performsanother iteration. The inventors contemplate numerous other similarimplementations that make use of the probability of the objects locationthat are suitable for use with the technology described herein.

In one alternative, the system can identify two or more players in asingle frame if those players are not likely to be confused from oneanother (e.g. players on opposite team benches, different sides of thefield, etc.). Central Computer 20 would determine that two or moreplayers are located apart from each other by more than a threshold basedon past and current location data, and send commands (via the RFController) to the two or more helmets to output at the same time inresponse to determining that two or more players are located apart fromeach other by more than the threshold. The cameras would simultaneouslysense the IR pulses from the multiple helmets and the camera computerswould find cluster of pixels for the multiple helmets in the capturedimage. The camera computers would send data packets for the multiplehelmets to Central Computer 20. Based on previous locations of the twoor more helmets, Camera Computer 20 will distinguish the cluster ofpixels of the two or more helmets in the captured image and determinenew locations for the two or more helmets based on the received IRpulses.

In one embodiment, the referees' hats can be instrumented witheffectively the same electronics that are in the helmet so that thereferrers can be tracked in the same manner as the players.

IV. Registration

Registration is the process of defining how to interpret data from asensor (a camera being one type of sensor). The sensors described aboveoutput data, for example, related to position. Since position isrelative, the system needs a reference from which to determine alocation. Thus, in order to be able to use positional data, the systemneeds to know how to interpret the positional data to make use of theinformation. One example of how to interpret data from different sensorsis to use the matrices described above. In that embodiment, defining howto interpret data includes determining suitable values for the variablesin the matrices.

FIG. 19 is a flow chart for registering the tracking system disclosedabove. In step 750, a coordinate system is established, which isaccomplished by establishing x, y, z axes with an origin (0,0,0). In oneembodiment, the origin is located at the corner of the football field;however other locations for the origin can also be used. For example, ina hockey rink, the origin could be at the center of the ice. In abasketball court, the origin could be at the center of the court or acorner of the court. Other locations for the origin can also be used. Instep 752, an initial educated guess is made at the parameter values forthe transformation matrix (J) based on experimentation and past use. Theguessed parameters will be improved upon later, so they need not beperfect at this time. In step 754, a set of landmarks are established. Alandmark is a known location in the coordinate system established instep 750 for which there is an IR emitting device (by increasing theshutter time the system can register to passive markings that would notbe typically considered IR emitters—like the white lines on the field.Alternatively, the system can remove the IR filter during theregistration process). The locations of the landmarks can be known dueto measuring them or due to placing them in known locations on the field(e.g., on a marked yard line). In one embodiment, the pylons at the fourcorners of both end zones can be used as landmarks by placing IRemitters on them or by increasing the shutter time to see the pylonswithout active IR emitters. These landmarks will be used with theprocess of FIG. 20.

In step 756, the three dimensional locations of the IR cameras/sensorsare determined. In one embodiment, they are measured. In step 758, oneor more absolute registration processes (FIG. 20) and (optionally) oneor more relative registration processes (FIG. 21) are performed. In someembodiments, the three dimensional locations of the IR cameras/sensorsare guessed at in step 752 and refined in step 758.

As described above, the system will use of a set of landmarks at knownlocations. Many different landmarks could be used. In one example, in anAmerican football game, the end zone on each side of the field has fourbright orange pylons. The location of these pylons can be measured aspart of step 754 of FIG. 19. Alternatively, other landmarks can be usedas long as the location is known. In one embodiment, IR emitting devicesare placed on the pylons. In an alternative embodiment, for example ahockey game, IR emitting devices can be placed in known locations on theice before the game and around the ice during the game. Otheralternatives can be used for different events.

FIG. 20 is a flowchart describing one embodiment of an absoluteregistration processes using landmarks. In step 780, each of the cameraswill capture an image which includes one or more landmarks. In oneembodiment, step 780 includes performing the process of FIG. 15. In step782, the data message (see step 522 of FIG. 15) is sent to the cameracomputer. Steps 780 and 782 can be performed for all or a subset ofcameras. In one embodiment, steps 780 and 782 are concurrently performedfor all cameras that can see any of the landmarks. In step 784, CentralComputer 20 will create a line of position for each landmark seen byeach camera using any of the processes described above. In step 786, thesystem will use the current set of camera parameters to determine thelocations that the LOPs intersect the field. Those locations will beconsidered initial locations of the landmarks. In step 788, the initiallocation of the landmarks determined in step 786 are compared to theknown locations for the landmarks. Note that step 786 and 788 areperformed for all landmarks seen by all the cameras that have seenlandmarks.

If the error between the known location of the landmarks and the newlydetermined location is less than the threshold, then the parameters usedin the previous iteration of step 786 are saved as the cameraparameters. If the error is not less than a threshold, then the cameraparameters (e.g., variables in the matrices above) are adjusted and theprocess loops back to step 786. In one embodiment, the error compared instep 788 is the sum of all the errors (absolute value or squared) forall the landmarks. In another embodiment, the error compared in step 788is the sum of all the errors for all the lines of position. In oneembodiment, the error compared in step 788 is the square root of the sumof the squares of the errors. Other calculations for aggregating errorcan also be utilized. The loop of step 786, 788 and 790 will becontinuously performed until the camera parameters are adjusted toreduce the error to below the threshold (or until no further significantimprovement is achieved).

In some embodiments, every camera will be able to see at least onelandmark. Therefore, the registration process will include performingthe processes of FIGS. 19 and 20. In another embodiment, there will besome sensors that will not see any landmarks. In that embodiment, someof the sensors will be registered using the process of FIG. 20, referredto as absolute registration, while other sensors will be performed usinga relative registration process. In the relative registration process, asensor is registered based on data from another sensor (effectivelyusing dynamic targets as landmarks).

FIG. 21 is a flowchart describing one embodiment of a relativeregistration process. In one example, some of the sensors are firstregistered using the process of FIG. 20. Subsequently, other sensors areregistered using the process of FIG. 21. During the event, the processesof FIGS. 20 and 21 can be repeated in any order throughout the event. Instep 820 of FIG. 21, the system will identify a set of one or morecameras/sensors that have not been registered in the latest absoluteregistration process and/or have not been updated in the currentregistration process of FIG. 21. That is, the system is identifyingwhich sensors need to be registered in the current performance of theprocess of FIG. 21. In step 822, the system will identify a set of datapoints (e.g., data packets about cluster of pixels in camera images)from the identified set of cameras from step 820 and one or more camerasthat were registered already in the latest absolute registrationprocess. That is data about the sensing of the same IR source isobtained from the identified set of cameras from step 820 and one ormore cameras that were registered already in the latest absoluteregistration process.

The process of FIG. 21 is based on comparing target position(s) seenfrom each camera for a number of frames. Because the system takes nearlytwo hundred frames per second and the system is seeing more than twentyplayers on the field and twice as many on the sideline, the system willacquire a rich data set from which to compare camera registrations. Thiswill be used to ensure consistency between registrations. In otherwords, lines of position should pass through the smallest possiblevolume of the target. Thus, in step 822, the system will identify datapoints (sensing of the same helmet) for multiple sensors where some ofthe sensors have been absolutely registered and some of them have notbeen registered properly yet or need to be updated (of course it'spossible also to register a camera against another camera that itselfwas registered in only a relative sense—so long as there is an absoluteregistration somewhere in the process). In step 824, lines of positionwill be created for each of those data points for each identifiedcamera. For each pair of lines of position with respect to a data point,the system will find the closest point of approach and distance Dbetween the pair of lines of position at that closest point of approach.In step 828, the system will determine whether the average distance D isless than the threshold. If not, then the current camera parameters areadjusted for the camera being relatively registered and the processmoves back to step 824. If the average distance is less than thethreshold, then the camera parameters are saved in step 832. In step834, the system determines whether there are any more cameras that needto be relatively registered using the process of FIG. 21. If not, theprocess of FIG. 21 is complete. If so, the process loops back to step820 and chooses the next set of cameras to relatively register. Even ifeach camera registration is better than the minimum threshold, thesystem may attempt further refinement to continue to improve itsregistration on a somewhat regular basis.

V. Ball Tracking

In addition to tracking players (moving or not), the system cansimultaneously track a moving ball. In one embodiment, the system willmanually track the ball. For example, a user using UI Computer 22 willuse a mouse (or other pointing device) to click on (or otherwise select)the player who is holding the ball. In one embodiment, the userinterface for the UI Computer 22 will include a list of players. Theuser of UI Computer 22 will simply click on the name of the player whocurrently holds the ball. Since the system knows the location of theplayer (or the player's equipment), the system can know the approximatelocation of the ball every time the player (or the player's equipment)is automatically identified. (and the system may interpolate balllocation when the user indicates possession changes. Such interpolationcould take advantage of physical modeling of gravity, wind resistance,etc.).

FIG. 22 is a flowchart describing an embodiment for manually trackingthe ball. In step 860, Central Computer 20 receives an indication of thepossession of an object. For example, the user clicks on the name of aplayer using UI Computer 22, and UI Computer 22 will transmit thatindication to Central Computer 20 that the selected player possesses theball at the specified moment in time. This can be converted into a 3Dlocation for the ball by doing a lookup of the associated playercoordinates. Additionally, other objects besides the ball can betracked. In step 862, Central Computer 20 will look up the location ofthe player (or the player's equipment) who is in possession of theobject/ball. In step 864, the location of the player is stored as thelocation of the object/ball for the current time. The system willmaintain a database that includes a set of locations of the object/balland the corresponding time for each location data point. In step 866, itis determined whether possession of the object/ball has changed. Thatis, the system will determine whether the object was associated with adifferent player in the previous iteration. If the previous locationdata was associated with another player, then the possession of theobject/ball has changed. If the previous location data was with the sameplayer as the current location data, then possession has not changed. Ifpossession has not changed, then the process of FIG. 22 is completed. Ifpossession has changed, then Central Computer 20 will access theprevious location for the object/ball. In step 872, Central Computer 20will interpolate intermediate location between the current location ofthe object/ball and the previous location of the object/ball using anyinterpolation method known in the art (including physical modeling ifappropriate) In step 872, the intermediate locations that were theresult of step 870 are stored in the database. The stored locationinformation for the object/ball can be reported in the same manner asdescribed above for the players. In one embodiment, the process of FIG.22 can be repeated continuously.

In another embodiment, the object/ball is tracked automatically. FIGS.8A and 8B, discussed above, provide hardware for automatically trackingthe ball. FIG. 23 is a flowchart describing one embodiment which can beused with the hardware of FIGS. 8A and 8B in order to automaticallytrack the ball or other moving object. In step 900, the sensor (e.g.RFID tag reader 202) will automatically detect the presence of an RFIDtag 208. That is, the RFID tag reader automatically senses that the ballis in proximity to the player (in possession of the player or near theplayer). Controller 200 of FIG. 8A will create a data packet with theplayer ID, RFID tag ID and current time. In some embodiments, the datapacket will not include time or the RFID tag number, particularly if theball is the only thing being tracked by RFID. In step 904, thecontroller will broadcast the data packet via radio module 204 so thatone or more listening stations (FIG. 8B) will receive the broadcast.Such listening stations may be included in the instrumentation carriedby the player. In such cases, the data would either be recorded locally,or re-transmitted to stations around the field. It's possible to sendthe “possession” message via coded blinks of the IR emitters as well asRF. In step 906, at least one RFID listening station detects thebroadcast and receives the data packet. In step 908, the one or morelistening stations that received the data packet send the data packet toCentral Computer 20 via Ethernet or other communication means. In step910, Central Computer 20 processes the data packet using the method ofFIG. 22. Central Computer 20 will be receiving multiple indications fromdifferent players during the event that the players are in possession ofthe ball. Simultaneously (or before or afterwards), Central Computer 20will also be automatically determining locations of multiple players(who are likely to be moving). Using the method of FIG. 22, CentralComputer 20 will store the location of a first player as the location ofthe ball in response to receiving an indication from the first playerthat the first player is in possession or proximity to the ball, andthen store the location of a second player as the location of the ballin response to receiving an indication from the second player that thesecond player is in possession or proximity to the ball. Intermediatelocations will be interpolated, as described by the process of FIG. 22.When two or more players indicate possession during the same frame, thesystem will likely use signal strength or last possession to determinecurrent possession. Alternatively, the system might compute the weightedcentroid based on signal strength from each such player. In someembodiments, the process of FIG. 23 is repeated continuously.

In an alternative embodiment, the ball can be instrumented withelectronics that are effectively the same as those in the helmet so thatthe ball can be tracked in the same manner as a helmet.

VI. Concussion Sensing

FIG. 6 depicts a helmet transponder circuit that includes a set ofaccelerometers 194 connected to (or are in communication with) processor184. FIG. 24 is a flowchart describing one embodiment of a method forautomatically detecting a concussion risk for a player wearing thehelmet that includes the circuit of FIG. 6. In step 950, processor 184will detect a change in motion based on data from the accelerometers. Instep 952, processor 184 will determine whether the change in motion issufficient to indicate a predefined force or acceleration. Based onexperimentation in a laboratory, it can be determined how much force oracceleration is necessary to indicate a concussion risk in an averageperson (or an average athlete). If the amount of force detected in step950 does not meet that predefined amount of force (step 954), thenprocessor 184 will not report a concussion risk or otherwise any changein the motion (step 956). Additionally, the system can maintain ahistory of impacts that might cumulatively indicate risk of braindamage. If the amount of force did meet the predefined amount of forcefor a concussion (step 954), then the processor 184 will store themotion data and the time it was recorded in step 958. There are twoembodiments disclosed in FIG. 24 for reporting the concussion data. Inone embodiment, when the player comes to a sideline (or any time orplace after the event), the helmet can be plugged into a computer viaUSB port connected to processor 184 in order to download the data. Forexample, in step 970, the helmet circuit is connected to a computer viaUSB port. In step 972, processor 184 will report the motion data to thecomputer. It would also be possible to query the helmet on the sidelinevia RF, IR, or other means. It's not necessary that it be plugged intothe computer directly.

In another embodiment, processor 184 can use radio module 182 toautomatically broadcast the data to a listening station (e.g. listeningstation of FIG. 8B or another device) during the event (or afterwards).Steps 960-964 of FIG. 24 include wirelessly reporting the information.For example, in step 960, the data, time and player ID is wirelesslytransmitted to camera computer by first transmitting it wirelessly to alistening station and then from the listening station to the CentralComputer 20 via Ethernet or other transport means. In step 962, CentralComputer 20 receives and stores the data, time and player ID. In step964, Central Computer 20 reports the concussion information to UIComputer 22. At that point, the operator of the UI Computer 22 caninform a coach or medical personnel using the user interface, sending atext message or email to the coach or medical personnel.

One embodiment includes wirelessly sending commands to the multipleobjects instructing different subsets of the multiple objects to reportat different times, outputting electromagnetic signals from the multiplemovable objects in response to respective commands, sensing theelectromagnetic signals from multiple movable objects, and calculatinglocations of the multiple objects based on the sensed electromagneticsignals from the multiple movable objects.

In one example implementation, the commands change dynamically duringthe event based on or more occurrence in the event. In another exampleimplementation, the commands change dynamically during the event byadding or removing one or more objects from the commands associated witha particular iteration.

In one embodiment, the system automatically chooses a first subset ofthe objects to track at a first frequency and automatically choosing asecond subset of the objects to track at a second frequency. Theoutputting and sensing are performed for the first subset of the objectsat the first frequency while the outputting, sensing and calculating areperformed for the second subset of the objects at the second frequencyin response to the automatically choosing the first subset and theautomatically choosing the second subset. Of course the system mightidentify and track any number of objects at any number of frequencies.For example, the system might track active players 5 times/second,benched players once every 2 seconds, the ball 3 times/second, refsonce/second, and fixed registration targets once every 10 seconds.

In one embodiment, the wirelessly sending commands to the multipleobjects comprises determining that two or more objects of the multipleobjects are located apart from each other by more than a threshold andsending commands to the two or more objects to output at the same timein response to determining that two or more objects are located apartfrom each other by more than the threshold, the sensing theelectromagnetic signals from multiple movable objects comprisescapturing an image and finding indications of the two or more objects inthe captured image, and the calculating locations of the multipleobjects includes distinguishing the indications of the two or moreobjects in the captured image based on previous locations of the two ormore objects and determining new locations for the two or more objectsbased on the indications of the two or more objects in the capturedimage. Alternatively, the system may at times track two or more objectsthat may not be separated by a minimum threshold, but where uniquelyidentifying the objects is not important. One such example might includetracking the referees.

One embodiment includes multiple objects each of which includes awireless receiver and a transmitter for providing an output, one or morewireless transmitters that send commands to the wireless receivers forthe multiple objects instructing different subsets of the multipleobjects to report at different times, object sensors that receive outputfrom the multiple objects, and a computer system in communication withthe object sensors, the computer system calculates locations of themultiple objects based on the sensed output from the multiple objects.

One embodiment includes wirelessly acquiring position samples ofmultiple objects that can move concurrently, calculating locations ofthe objects based on the position samples, wirelessly sendinginstructions to the objects that change timing of the position samples,wirelessly acquiring additional position samples of the set of objectsbased on the changed timing, and calculating new locations of theobjects based on the additional position samples.

One embodiment includes wirelessly sending commands to the multipleobjects instructing different subsets of the multiple objects to outputat different times, sensing output from the multiple movable objectsbased on the commands and calculating locations of the multiple objectsbased on the sensed output from the multiple movable objects.

One embodiment includes automatically determining locations of multiplemoving objects, automatically sensing that a first object of themultiple moving objects is in proximity of an item, identifying andstoring a location of the first object as a first location of theentity, automatically sensing that a second object of the multiplemoving objects is in proximity of the item, and identifying and storinga location of the second object as a second location of the item.

One embodiment includes multiple objects each of which includes one ormore local sensors and a transmitter. The sensors detect presence of anitem. The transmitters communicate presence of the item based onrespective one or more local sensors. The system further includes one ormore object sensors that sense position information about the multipleobjects, one or more receivers that receive one or more communicationsfrom one or more of the objects indicating presence of the item, and acomputer system in communication with the one or more receivers and theone or more object sensors. The computer system calculates locations ofthe multiple objects based on the sensed position information. Thecomputer system identifies a location of the item based oncommunications from one or more of the objects indicating presence ofthe item and the calculated locations of the multiple objects.

One embodiment includes means for automatically determining locations ofmultiple moving objects, means for automatically sensing that a firstobject of the multiple moving objects is in proximity of an item andsubsequently automatically sensing that a second object of the multiplemoving objects is in proximity of the item, and means for identifyingand storing a location of the first object as a first location of theentity in response to sensing that the first object of the multiplemoving objects is in proximity of the item, and for identifying andstoring a location of the second object as a second location of the itemin response to sensing that the second object of the multiple movingobjects is in proximity of the item.

One embodiment includes registering a first set of sensors using a setof landmarks detectable by the first set of sensors and registering asecond set of sensors based on the first set of sensors.

The foregoing detailed description of the invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The described embodiments were chosen in order to best explainthe principles of the invention and its practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

What is claimed is:
 1. A system for tracking players at a live sportingevent, comprising: a first set of transmitters associated with a firstset of players operable to transmit a first set of signals; a second setof transmitters associated with a second set of players operable totransmit a second set of signals; sensors positioned at the livesporting event operable to sense the first set of signals at a firstfrequency and the second set of the transmitters at a second frequency,wherein the first frequency and the second frequency are determinedbased on characteristics of the first set of players and the second setof players and wherein the sensors are operable to change frequency ofsensing for a transmitter in the first set of transmitters or the secondset of transmitters based on an event related to a player associatedwith the transmitter; and a computer system in communication with thesensors operable to calculate locations of the first set of playersbased on the first set of signals and calculate locations of the secondset of players based on the second set of signals.
 2. The system ofclaim 1, wherein the event is the player becoming an active player orgoing to the bench.
 3. The system of claim 1, wherein the event is theplayer lining up in a different position.
 4. The system of claim 1,wherein the event is the player changing proximity to a ball.
 5. Thesystem of claim 1, further comprising a referee transmitter associatedwith a referee, wherein the sensors are operable to sense a referee setof signals and the computer system is operable to calculate locations ofthe referee based on the referee set of signals.
 6. The system of claim1, further comprising accelerometers associated with the first set ofplayers and the second set of players operable to measure accelerationand transmit acceleration data to a processor.
 7. A system for trackingplayers at a live sporting event, comprising: transmitters associatedwith the players operable to transmit a first set of signals; a balltransmitter associated with a ball operable to transmit a ball signal;sensors positioned at the live sporting event to receive the signalsfrom the transmitters and the ball signal from the ball transmitter; anda computer system in communication with the sensors, wherein thecomputer system is operable to calculate locations of the players and alocation of the ball based on the signals sensed by the sensors.
 8. Thesystem of claim 7, wherein the computer system is operable to apply afilter to the first set of signals received from the transmitters,wherein the filter includes a noise filter and/or a filter whichdiscards signals originating from an exclusion zone at the live sportingevent.
 9. The system of claim 7, wherein the first set of signalsincludes a first signal with a first frequency associated with a firstsporting position at the live sporting event and a second signal with asecond frequency associated with a second sporting position at the livesporting event.
 10. The system of claim 7, wherein the computer systemis operable to calculate three-dimensional locations of the players anda three-dimensional location of the ball based on the signals sensed bythe sensors.
 11. The system of claim 10, wherein the three-dimensionallocations of the players are calculated up to 8 feet above a venue floorof the live sporting event and a three-dimensional location of the ballis calculated up to 50 feet above the venue floor of the live sportingevent.
 12. The system of claim 11, wherein the computer system isfurther operable to remove or exclude three-dimensional locations of theplayers based on historical data stored in a memory of the computersystem which indicates the three-dimensional locations are not accurate.13. The system of claim 7, wherein the computer system is operable tocreate an animation depicting motion of the players and/or the ball. 14.The system of claim 7, wherein the computer system is operable todetermine a change in possession of the ball among the players based onthe signals from the transmitters and the ball signal from the balltransmitter, wherein the computer system is further operable tointerpolate one or more intermediate locations between locations of theball determined using the ball signal from the ball transmitter.
 15. Asystem for tracking players at a live sporting event comprising: atransmitter associated with a player operable to transmit a signal toone or more sensors positioned at the live sporting event; and at leastone accelerometer in communication with a processor, wherein the atleast one accelerometer is operable to measure a change in motion andcommunicate the change in motion to the processor; and a computer incommunication with the processor; wherein the change in motion indicatesa force; wherein, upon the processor determining that the force isgreater than a threshold force, the processor is operable to send aconcussion risk message to the computer.
 16. The system of claim 15,wherein the computer is in wireless communication with the processor.17. The system of claim 15: wherein the computer includes a databasewith a history of impacts to a player; wherein, upon the processordetermining that the force is less than a threshold force, the processoris operable to send an impact message to the computer; and wherein thecomputer is operable to update the database with the history of impactsto the player to include impact data from the impact message.
 18. Thesystem of claim 15, wherein the computer includes a user interface (UI)with text message and/or email message functionality operable to send atext message and/or an email message to medical personnel or a coach.19. The system of claim 15, wherein the computer is in communicationwith the processor via Infrared (IR) or Radio Frequency (RF)communication.
 20. The system of claim 15, wherein the at least oneaccelerometer includes multiple accelerometers distributed around a headof the player.